The present invention relates in general to cellular communication networks and, more particularly, to a method and apparatus for assigning serving cell codes to cell sites within the network.
In a wireless cellular communication network, each cell site is assigned a group of radio frequency (RF) channels which may be used for communicating with mobile stations. However, due to the increasing popularity of wireless communications, RF channels must be reused among many different cell sites in order to accommodate users in high-traffic, population-dense areas, such as big cities.
The reuse of RF channels among the cell sites is determined according to a frequency reuse plan, which provides that cell sites that share a common channel or channel group must be sufficiently separated such that co-channel interference is kept at an acceptable level. In such a system, a mobile station operating on a particular channel may receive interfering signals on that channel from the co-channel site, and the mobile station needs to be able to distinguish between the serving channel and the interfering channel.
To deal with the co-channel interference problem, each cell site is assigned a serving cell code so that a mobile station can distinguish between a signal received from the serving cell site and an interfering signal received from a co-channel site, by using the serving cell codes. Thus, if two co-channel cell sites are close enough so that a mobile station might receive signals from both cell sites, then the cell sites must be assigned different serving cell codes.
A shortcoming of assigning serving cell codes is that the range of serving cell codes is usually limited. For example, for cellular digital packet data (CDPD), as defined in "Cellular Digital Packet Data System Specification," Release 1.0, Jul. 19, 1993, a group code color (GCC) is an example of a serving cell code, but only 32 group color codes are available. Thus, GCCs must not only be reused, but they may only be reused for co-channel sites if the cell sites are sufficiently spaced apart in a manner such that there is minimal co-channel interference between them. Presently, GCC assignment is performed manually by visually determining that two co-channel sites sharing the same GCC are far enough apart while referring to a site map of all of the cell sites that need to be assigned GCCs. However, manually assigning GCCs is extremely inefficient because it requires a significant amount of time and labor.